Solid particles

ABSTRACT

Solid particles containing 10 to 90 parts by weight of a dihydroxy compound and 10 to 90 parts by weight of a carbonic acid ester are disclosed. Also disclosed is a process for the production of these particles, an apparatus suitable for the process and a method for their use in production of polycarbonate by transesterification of carbonic acid esters with dihydroxy compounds.

The present invention relates to solid particles which contain dihydroxycompounds and carbonic acid esters and to a process for the productionthereof and to an apparatus for the production thereof and to the usethereof for the production of polycarbonate using thetransesterification process and to a process for the production ofpolycarbonate using the transesterification process.

It is known to produce polycarbonate by transesterifying carbonic acidesters with dihydroxy compounds. The process is described, for example,in the monograph by H. Schnell, Chemistry& Physics of Polycarbonate,Polymer Reviews, volume 9, John Wiley & Sons, 1964, pp. 44-51. Theprocess is also described in Encyclopedia of Polymer Science, volume 10,1969.

The process for the production of polycarbonate by transesterificationis in particular suitable for producing the bisphenol Ahomopolycarbonate. To this end, bisphenol A is transesterified withcarbonic acid esters, preferably diphenyl carbonate. The process for theproduction of polycarbonate by transesterification is also suitable forproducing copolycarbonates based on bisphenol A and further dihydroxycompounds as copolymerisation partners. To this end, bisphenol A and thefurther dihydroxy compounds are transesterified with carbonic acidesters, preferably diphenyl carbonate.

When producing polycarbonate by transesterification, the reactants(dihydroxy compounds and carbonic acid esters and optionally furtherauxiliary substances and additives, such as for example branchingagents) are reacted in a multistage reaction, preferably as a melt,preferably with the addition of a transesterification catalyst or acombination of two or more transesterification catalysts withelimination of a hydroxy compound from the carbonic acid ester. Ifdiphenyl carbonate is used as the carbonic acid ester, the hydroxycompound eliminated is phenol. The equilibrium of the reaction issteadily displaced by varying the temperature and pressure above thereaction mixture. In this manner, light-coloured, solvent-freepolycarbonates may be obtained by continued condensation

Numerous catalysts, embodiments of the process and of the apparatus usedhave been described for the transesterification process for theproduction of polycarbonates.

The transesterification process for the production of polycarbonates hasthe advantage that neither solvents nor phosgene are required, as is thecase with the “phase interface process” for the production ofpolycarbonates. The transesterification process for the production ofpolycarbonates thus allows polycarbonate to be produced in an economicaland environmentally friendly manner, which polycarbonate additionallyhas the advantage that it contains no chlorine.

The process for the production of polycarbonate by transesterificationgenerally places stringent requirements upon the purity of the startingmaterials and of the auxiliary substances used. Even the particularpresentation of the starting materials and the auxiliary substances mayhave an influence upon the process and the quality of the polycarbonateproduced.

The raw materials, dihydroxy compounds and carbonic acid esters used inthe process for the production of polycarbonates by transesterificationare, for example, introduced into the process as separate components andmixed, for example, during melting of the components. They may also bothbe introduced into the process as melts, such that the melts are mixedbefore the reaction. Such processes are described, for example, in EP-A0 861 863.

A melt of a dihydroxy compound may be cooled to produce granules, flakesor prills in order to facilitate packaging, transport and storage,wherein prills exhibit advantages over granules or flakes due to theirlower dust content and better flow characteristics.

It is known to produce solid particles, for example “prills”, whichcontain only one material for the production of polycarbonates by thetransesterification process, for example bisphenol A.

Prills of dihydroxy compounds, in particular bisphenol A prills, may forexample be produced by introducing molten dihydroxy compounds, inparticular molten bisphenol A, into the top of a prilling tower via aspray head having a plurality of nozzles, into which prilling tower isintroduced a countercurrently recirculated stream of cooling gas,wherein the prills which have cooled approximately to room temperatureare collected at and discharged from the bottom of the prilling tower.

JP-6-107 581 discloses a process for the production of bisphenol Aprills in which molten bisphenol A is introduced into the top zone of aprilling tower and cooling gas is introduced countercurrently at thebottom of the prilling tower, which gas draws the heat of fusion fromthe falling droplets of melt. The solidified prills are discharged fromthe bottom of the prilling tower.

Separate storage and separate transport of the two raw materials,dihydroxy compound and carbonic acid ester, for the process for theproduction of polycarbonate by transesterification entail significantlogistical costs. Separate introduction of the two raw materials intothe process for the production of polycarbonate by transesterificationis likewise associated with elevated plant and equipment costs.

The object underlying the present invention was accordingly to provide aprocess for the production of polycarbonate by transesterification ofdihydroxy compounds and carbonic acid esters, which process does notexhibit the disadvantages arising from the use of the two separate rawmaterials, dihydroxy compounds and carbonic acid esters, of theprocesses known from the prior art.

Said object of the invention is achieved by a process for the productionof polycarbonate by transesterification of dihydroxy compounds andcarbonic acid esters, wherein the dihydroxy compounds and the carbonicacid esters are introduced into the process in the form of solidparticles which contain both dihydroxy compounds and carbonic acidesters.

The present invention accordingly provides a process for the productionof polycarbonate by transesterifying carbonic acid esters with dihydroxycompounds, characterised in that the raw material used comprises solidparticles which contain 10 to 90 parts by weight of a dihydroxy compoundand 10 to 90 parts by weight of a carbonic acid ester.

It is possible in this process that further raw materials, other thanthe stated solid particles, are used for the process according to theinvention. These may also comprise further dihydroxy compounds and/orcarbonic acid esters. It is preferred to introduce the entire quantityof carbonic acid ester and dihydroxy compound required as startingmaterial in the form of the solid particles according to the invention.

The present invention furthermore provides the use of solid particleswhich contain 10 to 90 parts by weight of a dihydroxy compound and 10 to90 parts by weight of a carbonic acid ester for the production ofpolycarbonate by transesterification of carbonic acid esters withdihydroxy compounds.

The present invention furthermore provides solid particles,characterised in that they contain 10 to 90 parts by weight of adihydroxy compound and 10 to 90 parts by weight of a carbonic acidester.

The present invention furthermore provides a process for the productionof solid particles, characterised in that a melt which contains 10 to 90parts by weight of the dihydroxy compound and 10 to 90 parts by weightof the carbonic acid ester is cooled.

The present invention furthermore provides an apparatus for theproduction of solid particles which contain 10 to 90 parts by weight ofa dihydroxy compound and 10 to 90 parts by weight of a carbonic acidester, characterised in that the apparatus has two separate feed linesfor the melt of the carbonic acid ester and for the melt of thedihydroxy compound and that these feed lines open into two separate heatexchangers and that the lines to convey the carbonic acid ester and thedihydroxy compound away from their particular heat exchangers are joinedto combine the two streams of material and that, in the line whichconveys onwards the combined streams of material comprising carbonicacid ester and dihydroxy compound, the apparatus has a mixing elementand, thereafter, a heat exchanger and that the apparatus comprises aprilling tower which is fed with the combined stream of materialcomprising carbonic acid ester and dihydroxy compound originating fromthe last-stated heat exchanger.

The process according to the invention for the production ofpolycarbonate by transesterification has numerous advantages. Itsimplifies raw materials logistics, in particular simplifying storageand transport of the raw materials. Introduction of the raw materialsinto the process is simplified

The process according to the invention for the production ofpolycarbonate by transesterification using the solid particles accordingto the invention as the raw material is distinguished by logisticaladvantages, such as for example simple storage of the raw materials,simple transport of the raw materials and simple introduction of the rawmaterials into the process.

The process according to the invention for the production ofpolycarbonate by transesterification using the solid particles accordingto the invention as the raw material is furthermore distinguished by theadvantage that the precise stoichiometric ratio between the carbonicacid ester and dihydroxy compound may be established in the prill. Thisfurthermore has the advantage that complex apparatuses for mixing themelts or solids consisting of the dihydroxy compound and carbonic acidester are not required in the process for the production of thepolycarbonate.

The solid particles of dihydroxy compounds and carbonic acid estersaccording to the invention have numerous advantages. They aremechanically stable. They may be stored without reacting chemically ordiscolouring. The solid particles according to the invention aredistinguished by elevated colour stability and long storage life as wellas by elevated purity.

The process according to the invention for the production of solidparticles which contain carbonic acid esters and dihydroxy compounds hasnumerous advantages. It provides mechanically stable, storable andlight-coloured solid particles of the stated composition in a simplemanner. In comparison with separate preparation of the carbonic acidester and the dihydroxy compound, less plant and equipment is required,for example one prilling tower instead of two prilling towers.

The apparatus according to the invention for the production of solidparticles which contain carbonic acid esters and dihydroxy compounds hasnumerous advantages.

For example, the apparatus according to the invention ensures that thestreams comprising the carbonic acid ester melt and the melt of thedihydroxy compound are not combined until they have been cooled to atemperature just above the particular melting point thereof. This meansthat the two melts are combined at the lowest possible temperature,which in turn means that unwanted secondary reactions do not occur. Theapparatus according to the invention furthermore ensures that the meltstreams combined in this manner are thoroughly mixed immediately afterthey have been combined and are cooled in another heat exchanger to atemperature just above the melting point of the mixture. Prillproduction and thus cooling then proceed immediately thereafter. Theapparatus according to the invention thus ensures the shortest possibleresidence time of the combined melts at the lowest possibletemperatures, so reducing unwanted secondary reactions to a minimum.

The solid particles according to the invention may be of any desiredsize and shape. They are preferably of a spherical or virtuallyspherical shape (“prills”). They may, however, assume the form of powderparticles, flakes or pellets.

The process according to the invention for the production of solidparticles containing dihydroxy compounds and carbonic acid esters ischaracterised in that a melt, which contains dihydroxy compounds andcarbonic acid esters, is cooled and consequently solidified. Thisprocess is preferably performed by “prilling”, i.e. the melt isdispersed in the gas phase, for example in the form of spherical meltparticles, which then cool in free fill in the gas phase and solidify.Solidification preferably means crystallisation. It may, however, alsomean in general crystallisation or glassy solidification which resultsin the solid particles' having an amorphous state.

The stated, preferred embodiment according to the invention of theprocess for the production of solid particles by the prilling processhas the advantage that the prilling process permits a short residencetime of the combined streams of dihydroxy compound and carbonic acidester as a melt. This is ensured by its being possible to achieve rapidcooling and solidification of the combined melts of carbonic acid esterand dihydroxy compound in the prilling process. This results in theadvantage that the individual components, carbonic acid esters anddihydroxy compounds, do not react with each other in the melt, such thatno unwanted secondary products are obtained. The stated advantagedistinguishes the prilling process from other processes for solidifyingthe melt, for example processes for producing granules or flakes.

It is accordingly a particularly preferred embodiment of the processaccording to the invention for the production of solid particles if theprocess is performed as a prilling process and if the process has onlyshort residence time of the combined melts of dihydroxy compound andcarbonic acid ester and if the combined melt of carbonic acid ester anddihydroxy compound has a temperature which is only slightly above thesolidification point of this melt.

The residence time of the combined melts of dihydroxy compound andcarbonic acid ester is preferably less than 60 seconds, particularlypreferably less than 30 seconds and very particularly preferably lessthan 10 seconds. The temperature of the combined melts of carbonic acidester and dihydroxy compound is preferably less than 20° C. above thesolidification point of this melt, particularly preferably less than 5°C. above the solidification point and very particularly preferably lessthan 1° C. above the solidification of this melt.

One particularly preferred embodiment of the process according to theinvention is accordingly to prepare the separate melts of dihydroxycompound and carbonic acid ester each separately at a temperature justabove the melting point thereof, then to mix them, then to cool them toa temperature just above the solidification point of the mixed melt andthen to solidify them in a prilling process, wherein the entire processis performed such that the residence time of the combined melt ofcarbonic acid ester and dihydroxy compound in the liquid phase, i.e.until solidification by prilling, is kept as short as possible.

Another preferred embodiment of the process according to the inventionfor the production of the solid particles is to solidify the melt whichcontains dihydroxy compounds and carbonic acid esters using knownprocesses to yield granules or flakes.

Another preferred embodiment of the process according to the inventionfor the production of the solid particles is to pelletise a melt whichcontains dihydroxy compounds and carbonic acid esters using knownpelletising processes.

Dihydroxy compounds for the purposes of the present invention are anydesired dihydroxy compounds which are suitable for the production ofpolycarbonates.

The following are examples of suitable dihydroxy compounds:

4,4′-dihydroxydiphenyl,

2,4-bis(4hydroxyphenyl)-2-methylbutane,

1,1-bis(4-hydroxyphenyl)ryclohexane,

α,α-bis(4hydroxyphenyl)-p-diisopropylbenzene,

α,α-bis(4-hydroxyphenyl)-m-diisopropylbezene,

2,2-bis(3-methyl-4-hydroxyphenyl)propane,

2,2-bis(3-chloro-4-hydroxyphenyl)propane,

bis(3,5-dimethyl-4-hydroxyphenyl)methane,

2,2-bis(3,5-dimethyl-hydroxyphenyl)propane,

bis(3,5-dimethyl-4-hydroxyphenyl) sulfone,

2,4-bis(3,5-dimethyl-4-hydroxyphenyl)-2-methylbutane,

1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane,

α,α-bis(3,5-dimethyl-4-hydroxyphenyl)-p-diisopropylbenzene,

1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,

1,1-bis(4-hydroxyphenyl)-3-methylcyclohexane,

1,1-bis(4-hydroxyphenyl)-3,3,-methylcyclohexane,

1,1-bis(4-hydroxyphenyl)-4-methylcyclohexane,

2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,

2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane,

1,1-bis(4-hydroxyphenyl)-1-phenylethane,

2,2-bis(3,5-dimethyl-4-hydroxyphenyl)-2-phenylethane,

2,2-bis(4-hydroxyphenyl)-2,2-diphenylethane,

9,9-bis(4-hydroxyphenyl)fluorene,

9,9-bis(3,5-dimethyl-4-hydroxyphenyl)fluorene.

The following are particularly preferred dihydroxy compounds:

2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,

1,1-bis(4-hydroxyphenyl)cyclohexane,

1-bis(4-hydroxyphenyl)-1-phenylethane,

1,1-bis(4hydroxyphenyl)-3,3,5-trimethylcyclohexane,

1,1-bis(4-hydroxyphenyl)-3-methylcyclohexane,

1,1-bis(4-hydroxyphenyl)-4-methylcyclohexane,

9,9-bis(3,5-dimethyl-4-hydroxyphenyl)fluorene.

2,2-Bis(4-hydroxyphenyl)propane (also known as bisphenol A) is thedihydroxy compound which is particularly preferred according to theinvention.

According to the invention, any desired carbonic acid esters may beused. Diphenyl carbonate is preferred.

The solid particles according to the invention contain 10 to 90 parts byweight of a dihydroxy compound and 10 to 90 parts by weight of acarbonic acid ester. The solid particles according to the inventionpreferably contain 30 to 80 parts by weight of a dihydroxy compound and20 to 70 parts by weight of a carbonic acid ester. The solid particlesaccording to the invention particularly preferably contain 0.9 to 1.2mol of carbonic acid ester per mol of dihydroxy compound. The solidparticles very particularly preferably consist of 1 mol of dihydroxycompound and 1 mol of carbonic acid ester without containing any furthersubstances. The person skilled in the art is, of course, aware that, asin the past, the solid particles may contain small quantities ofimpurities. The phrase “further substances” is thus not intended to meansuch impurities, but merely that no appreciable quantity of any furthersubstances is deliberately included in the solid particles, suchsubstances possibly being, for example, regulators, fillers or any otherdesired substances. Among the above-stated solid particles, those whichare most preferred are those in which the hydroxy compound is bisphenolA and the carbonic acid ester is diphenyl carbonate.

The process for the production of polycarbonate by transesterifyingdihydroxy compounds and carbonic acid ester is performed in accordancewith known methods, wherein, in contrast with the prior art, the solidparticles according to the invention which contain dihydroxy compoundsand carbonic acid esters are used as the raw material. Preferably, theentire required quantity of dihydroxy compounds and carbonic acid estersis used in the form of the solid particles according to the invention.It is, however, also possible to introduce dihydroxy compounds and/orcarbonic acid esters in another form, for example as a melt or as asolution or as a solid, into the process in addition to the solidparticles according to the invention.

Polycarbonates according to the invention which are produced using theprocess according to the invention for the production of polycarbonateby transesterification are both homopolycarbonates and copolycarbonates.

Preferred polycarbonates are bisphenol A homopolycarbonate andcopolycarbonates which contain bisphenol, A and1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane as the dihydroxycomponents.

Bisphenol A homopolycarbonate is particularly preferred.

The apparatus according to the invention is illustrated in greaterdetail below by means of a drawing (FIG. 1) showing a preferredexemplary embodiment.

FIG. 1 shows an apparatus which has two separate feed lines 1 and 2 forthe separate melt streams of carbonic acid ester and dihydroxy compound.The feed lines each lead into the heat exchangers 3 and 4, in which theseparate melts are cooled to just above the respective solidificationpoints thereof. The combined melt streams are then passed through amixer 5 and cooled in a heat exchanger 6 to a temperature just above thesolidification point of the combined melt stream of carbonic acid esterand dihydroxy compound. This melt is then introduced via a spray head 7into a prilling tower 8 in the form of liquid drops, wherein nitrogen 10flows countercurrently to these drops, which nitrogen is introduced intothe bottom is of the prilling tower via an annular nozzle 9. The solidprills of carbonic acid ester and dihydroxy compound 11 are drawn offfrom the bottom of the prilling tower.

EXAMPLES Example 1

The following Examples show that, with regard to the use of mixed prillsof dihydroxy compounds, in particular bisphenol A (BPA) and carbonicacid esters, in particular diphenyl carbonate (DPC), as a raw materialin the process for the production of polycarbonate bytransesterification, it is possible to produce mixed prills of dihydroxycompounds, in particular bisphenol A (BPA) and carbonic acid esters, inparticular diphenyl carbonate (DPC), and whether storage of such prillsover an extended period is possible without increased elimination of ahydroxy compound, in particular phenol.

To this end, a 50:50 wt. % mixture of DPC and BPA was homogenised bymelting at 140° C. under an inert gas atmosphere. Prills were thenobtained under laboratory conditions by dropwise addition of the meltinto liquid nitrogen and slow warming to room temperature. These prillshad a diameter of approx. 1 mm with an approximately spherical shape,were pourable and no surface tack was observed.

The test was performed both without addition of a catalyst (sample A)and in the presence of 500 ppb of sodium phenolate (addition immediatelybefore dropwise addition into liquid nitrogen, sample B). Thecomposition of the resultant prills was determined by HPLC immediatelyafter production and after 2 and 4 weeks' storage at room temperatureunder an air atmosphere. The solidified 50:50 melt from sample A(unprilled, blank sample) was used as a comparison sample.

Table 1 summarises the results. In addition to BPA and DPC, smallquantities of phenol and corresponding quantities of low condensationproducts y1, x1 and n1 were found in all the samples. Within theaccuracy of measurement, the sample A prills exhibited the samehomogeneity (BPA:DPC ratio) and composition as the blank sample. Nofighter reaction during storage was observed, condensation thus havingoccurred during the melting operation. In the presence of 0.5 ppm ofsodium phenolate, increased condensation was observable immediatelyafter prilling and stabilised to approx. 3% conversion after 2 weeks'storage. There was no detectable formation of yellow components in anyof the samples after 4 weeks' storage.

TABLE 1 Composition of the BPA/DPC samples (All values in wt. %,optimised for detection of secondary components. 0.18% of o,p-BPA wasadditionally detected in each case.) Com- Com- Com- pound pound poundSample Time BPA DPC Phenol y1 x1 n1 Blank im- 49.5 49.6 0.4 0.6 <0.010.01 mediate Blank 14 d 49.7 49.7 0.3 0.6 <0.01 0.02 Blank 28 d 49.749.3 0.3 0.6 <0.01 0.02 Sample A im- 49.7 49.9 0.2 0.8 <0.01 0.02mediate Sample A 14 d 49.5 49.8 0.3 0.8 <0.01 0.03 Sample A 28 d 49.649.2 0.3 0.7 <0.01 0.03 Sample B im- 48.3 48.4 0.8 2.8 0.10 0.12 mediateSample B 14 d 46.8 47.1 1.3 5.1 0.12 0.13 Sample B 28 d 46.9 46.8 1.45.5 0.12 0.14

These Examples show that it is possible to produce mixed prills of BPAand DPC, that the rates of conversion in the quenched melts at roomtemper are very low in the absence of catalytically active compounds,that no colour formation is to be observed. It is favourable to keep theresidence time of the melt before prilling as short as possible and toensure strict exclusion of catalytic compounds.

Example 2 Production of Polycarbonate from DPC/BPA Mixed Prills

Methods used: Relative solution viscosity eta_(rel) was determined on asolution containing 5 g/l of polymer in dichlommethane at 25° C.

The yellowness index YI was measured to ASTM D 1925, transmission toASTM D 1003.

A mixture of 22.6 g (53.0 mmol) of diphenyl carbonate and 22.8 g (50.0mmol) of bisphenol A were homogenised by being fused at 140° C. under anitrogen atmosphere. Approximately spherical prills (diameter approx.1.0 mm) were then obtained by dropwise addition of the melt into liquidnitrogen and slowly raising the temperature to room temperature. Theprills were pourable and no surface tack was observed even after 14days' storage at room temperature.

35 g of the prills produced in this manner were placed in a 50 mlthree-necked flask equipped with stirrer, internal thermometer andVigreux column and distillation bridge. Atmospheric oxygen was removedfrom the apparatus by fivefold application of a vacuum and subsequentflushing with nitrogen (99.99%) and the mixture was heated to 150° C.Fusion of the BPA/DPC mixed prills was complete at this temperature.After addition of 4×10⁻³ mol% of tetraphenylphosphonium phenolaterelative to bisphenol A, the temperature was raised stepwise to 250° C.and the liberated phenol removed by distillation at 100 mbar. The vacuumwas then enhanced stepwise to 1 mbar and the temperature increased to260° C. The temperature was then increased to 300° C. and the mixturestirred for 1.5 hours at a vacuum of 0.1 mbar. The liberated phenol wascondensed in the distillation bridge and remove& The entire test lasted3.5 h from fusion of the mixed prills.

Light-coloured, solvent-fee polycarbonate exhibiting a relative solutionviscosity eta_(rel) of 1.260 was obtained as the result of the reaction.The YI of the sample was determined at 2.3 and transmission at 88.31%.The range of properties of the polycarbonate produced in this mannercould not be distinguished from that of polycarbonate which had beenproduced by introducing the raw materials DPC and BPA into the processas separate substances.

What is claimed is:
 1. Solid particles, characterised in that theycontain 10 to 90 parts by weight of a dihydroxy compound and 10 to 90parts by weight of a carbonic acid ester.
 2. Solid particles,characterised in that they contain 10 to 90 parts by weight of bisphenotA and 10 to 90 parts by weight of diphenyl carbonate.
 3. Process for theproduction of solid particles according to claim 1, characterised inthat a melt which contains 10 to 90 parts by weight of the dihydroxycompound and 10 to 90 parts by weight of the carbonic acid ester iscooled.
 4. Process for the production of solid particles according toclaim 2, characterised in that a melt which contains 10 to 90 parts byweight of bisphenol A and 10 to 90 parts by weight of diphenyl carbonateis cooled.
 5. Apparatus for the production of the solid particlesaccording to claim 1, characterised in that the apparatus has twoseparate feed lines for the melt of the carbonic acid ester (1) and forthe melt of the dihydroxy compound (2) and that these feed lines openinto two separate heat exchangers (3 and 4) and that the lines to conveythe carbonic acid ester and the dihydroxy compound away from theirparticular heat exchangers are joined to combine the two streams ofmaterial, and that, in the line which conveys onwards the combinedstreams of material comprising carbonic acid ester and dihydroxycompound, the apparatus has a mixing element (5) and, thereafter, a heatexchanger (6) and that the apparatus comprises a prilling tower (8)which is fed with the combined stream of material comprising carbonicacid ester and dihydroxy compound originating from the last-stated heatexchanger.
 6. A process for the production of solid particles comprisingobtaining a melt that contains 10 to 90 parts by weight of the dihydroxycompound and 10 to 90 parts by weight of the carbonic acid ester andcooling the melt.
 7. The process of claim 6 wherein the dihydroxycompound is bisphenol A and where carbonic acid ester is diphenylcarbonate.
 8. A process for the production of solid particles comprisingobtaining a melt which contains 10 to 90 parts by weight of bisphenol Aand 10 to 90 parts by weight of diphenyl carbonate and cooling said meltcharacterized in that it is carried out in an apparatus having twoseparate feed lines for the melt of the carbonic acid ester and for themelt of the dihydroxy compound and that these feed lines open into twoseparate heat exchangers and that the lines to convey the carbonic acidester and the dihydroxy compound away from their particular heatexchangers are joined to combine the two streams of material, and that,in the line which conveys onwards the combined streams of materialcomprising carbonic acid ester and dihydroxy compound, the apparatus hasa mixing element and, thereafter, a heat exchanger and that theapparatus comprises a prilling tower which is fed with the combinedstream of material comprising carbonic acid ester and dihydroxy compoundoriginating from the last-stated heat exchanger.
 9. A method of usingthe solid particles according to claim 1 comprising producingpolycarbonate by transesterification of carbonic acid esters withdihydroxy compounds.